一、大概思路

　　1、從cookie中取商品列表

　　2、判斷要添加的商品是否存在cookie中。

　　3、如果已添加過，則把對應的商品取出來，把要添加的商品的數量加上去。

　　4、如果沒有添加過，則把改商品添加到商品列表中。

　　5、再把商品列表序列化，加入cookie中。

二、代碼實現

　　1、定義一個購物車商品的pojo

public class CartItem {

    private Long id;

    private String title;

    private Long price;

    private Integer num;

    private
 
 String image;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Long getPrice() {
        
 
return price;
    }

    public void setPrice(Long price) {
        this.price = price;
    }

    public Integer getNum() {
        return num;
    }

    public void setNum(Integer num) {
        this.num = num;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        
 
this.image = image;
    }
}

　　2、定義一個購物車的接口和實現類

public interface CartService {

    TaotaoResult addCartService(HttpServletRequest request, HttpServletResponse response, Long itemId, Integer num);
}

@Service
public class CartServiceImpl implements CartService {

    @Autowired
    private ItemService itemService;
    @Value("${COOKIE_EXPIRE}")
    private Integer COOKIE_EXPIRE;

    @Override
    public TaotaoResult addCartService(HttpServletRequest request, HttpServletResponse response, Long itemId, Integer num) {
        // 1.從cookie中取商品列表
        List<CartItem> list = getCartFromCookie(request);
        // 2.判斷是否已經添加過購物車
        boolean haveflag = false;
        for (CartItem c : list) {
            //3.如果添加過,把對應的商品取出來，數量加Num
            if(c.getId().longValue() == itemId) {
                c.setNum(c.getNum() + num);
                haveflag = true;
                break;
            }
        }
        // 4.如果沒添加過,則把該商品添加進去。
        if (!haveflag) {
            TbItem item = itemService.getItemById(itemId);
            CartItem cartItem = new CartItem();
            cartItem.setNum(num);
            cartItem.setId(itemId);
            cartItem.setPrice(item.getPrice());
            cartItem.setTitle(item.getTitle());
            if (item.getImage() != null) {
                String image = item.getImage();
                String[] strings = image.split(",");
                cartItem.setImage(strings[0]);
            }
            list.add(cartItem);
        }
        // 5.再把list返回到cookie中
        CookieUtils.setCookie(request, response, "TT_CART", JsonUtils.objectToJson(list), COOKIE_EXPIRE);
　　　　　　
        return TaotaoResult.ok();
    }

    private List<CartItem> getCartFromCookie(HttpServletRequest request) {
        try {
            String json = CookieUtils.getCookieValue(request, "TT_TOKEN", true);
            List<CartItem> list = JsonUtils.jsonToList(json, CartItem.class);
            if (list == null) {
                return new ArrayList<>();
            }else {
                return list;
            }
        }catch (Exception e) {
            return new ArrayList<>();
        }
    }
}

　　3、controller來接收前端的請求，並響應到cart-success.jsp頁面。

@Controller
public class CartController {

    @Autowired
    private CartService cartService;

    @RequestMapping("/cart/add/{itemId}")
    public String addCart(@PathVariable Long itemId, Integer num, HttpServletRequest request, HttpServletResponse response) {
        TaotaoResult result = cartService.addCartService(request, response, itemId, num);
        return "cart-success";
    }
}

cookie來實現購物車功能